• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.9 no.2
• /
• pp.112-121
• /
• 1997

This study is focused on the development and selection of optimal cool tube system to maximize its thermal performance. Cool tube is devised to reduce the heating and cooling load of building by preheating or refreshing of intake air. Finite volume method was adopted to solve the conduction problem between the cool tube and earth. We examine the cool tube system for two operating periods, a short term(12 hours) and a long term(3 months). The results of short term operations reveal that condensation significantly influences and raises the exit air temperature. For long term operations, optimum conditions of cool tube system are obtained with variations of flow-rate, depth, length and diameter of cool tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.3 no.2
• /
• pp.131-141
• /
• 1991

A method of optimum design of an axial rotary sensible heat exchanger for the heat recovery of exhaust gas from the air conditioning space was developed in consideration of economics of investment cost and profit according to the installation of heat exchangers. Leakage rate of exhaust gas was calculated and the correlation for the pressure drop due to leakage of exhaust gas was proposed. Heat transfer between the matrix and exhaust and intake gas was analysed to calculate the effectiveness of heat exchanger, which was used for the optimum design of rotary heat exchanger. The results show that optimum rotational speed increases as the length of rotor increases and there exists optimum NTU which maximizes the gain of total cost according to the installation of rotary heat exchanger.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1317-1322
• /
• 2004

In this report, the heat transfer model of spray cooling on hot surface was developed by focusing on the effect of rebound motion of droplets. In the model, it was assumed that droplets rebound repeatedly on the hot surface and heat transfer upon droplet impact is proportional to sensible heat which heats up the droplets to the saturation temperature. In addition, to take account of the contribution of th heat flux upon impact of rebound droplets, it was assumed that the rebound droplets are distributed following the Gaussian distribution from 0 to L, which distance L is determined by maximum flight distance $L_{max}$. Also the calculated results were compared with existing experimental results.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1996.10b
• /
• pp.77-80
• /
• 1996

우리나라에서 피크부하용으로 사용하는 복합발전이 하계시에서 외기온도가 상승함에 따라 실제로는 정격출력을 내지 못하고 있다. 따라서 본 연구에서는 연료(LNG)의 냉열을 이용하여 가스터빈의 연소용공기를 냉각시킬 경우, 복합발전 시스템의 성능변화를 분석하기 위하여 시뮬레이션을 수행하였다. 그 결과 LNG의 냉열을 이용하여 연소용공기를 원하는 온도까지 냉각시킬 수 있음을 확인할 수 있었다. 또한 연소기로 연료를 투입하기전에 설계온도까지 예열시키는 열교환기를 통해 배기가스에 함유된 현열을 더욱 많이 회수하면서, 가스터빈 투입연료의 온도를 상승시킬 수 있어, 시스템효율이 더욱 상승함을 알 수 있었다. 결론적으로 외기온도가 변하는 경우에, 본 시스템의 도입을 위해서는 경제성분석과 더불어 열교환기 시스템의 최적합성이 추후 진행되어야 할 것이며, 이를 통해 최적의 발전시스템을 구성할 수 있으리라 생각된다.

• Journal of Environmental Science International
• /
• v.9 no.2
• /
• pp.109-114
• /
• 2000

The purpose of the present study is to develope the estimation scheme for sensible heat flux by semi-empirical approach using routine meteorological data such as solar radiation and air temperature. To compare observed sensible heat flux with estimated sensible heat flux, the sensible heat fluxes were measured by three dimensional sonic anemometer-thermometer. The field observation was performed during 1 year from December 1, 1995 to November 30, 1996 on a rice paddy field in Chunchon basin. The heat fluxes were measured at a heights of 5m and mean meteorological variables were obtained at two levels, 2.5m(or 1.5m) and 10m. Since condition of rice paddy field such as, wetness of the field, roughness length, vary widely, we devided annual data to 5 periods. Comparing with two sensible heat fluxes, the results showed that the correlation coefficients were more than 0.86. Thus, we can conclude that the estimation method of sensible heat fluxes using routine meteorological data is practical and reliable enough.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.2 s.233
• /
• pp.287-293
• /
• 2005

In the present study, to determine the flow rate of droplets supplied to heat transfer surface after (j-1)th rebound, $D_X[j{\ge}2]^{\ast}$, it was assumed that the rebound droplets are distributed according to the Gaussian distribution from 0 to L, in which the flight distance L is determined by maximum flight distance $L_{max}$. We also assumed that $L_{max}$ is dependent on the air flow velocity and mean size of droplets. The local heat flux of a dilute spray in high temperature region was predicted using the newly evaluated $D_X[j{\ge}2]^{\ast}$. In addition, the predicted results by the present model were compared with the existing experimental data.

• Solar Energy
• /
• v.18 no.1
• /
• pp.45-55
• /
• 1998

태양열이나 심야전력과 같이 에너지의 공급과 수요가 시차적으로 다를 경우 축열저장이 필수적이다. 축열조는 부하에 따라 그 부피가 커지게 되고 부피는 곧 경제성과 밀접한 관계를 갖고 있다. 따라서 이 연구는 축열조의 소형화에 관한 연구로 이번 실험에서 수행된 Nodule S-64(PCM-NaOH)인 구형 볼타잎을 사용하였고, 260Lit 용량의 축열조를 설계 제작하여 수학적 모델링과 실험을 병행하였다. 실험에 사용한 S-64는 이번 실험을 위해 제작한 것으로 축열 결과 현열인 물의 경우보다 축열량이 두배로 증가하였다. 따라서 기존 축열조 부피를 절반정도 축소가 가능하며, 운전조건에 따라 더이상 줄일 수도 있어 태양열이나 심야전력용 축열조로 매우 적합함을 알 수 있었다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.2 no.2
• /
• pp.85-98
• /
• 1990

Method of optimum design of a compact sensible plate-fin heat exchanger for the heat recovery of exhaust gas from the air conditioning space was developed in consideration of the econamics of investment cost and profit according to the installation of heat exchanges. In the counterflow heat exchanger, the frontal area was fixed and the length of heat exchanger was optimized in order to maximize the net gain according to the setting of the heat exchanger. In the cross flow heat exchanger, the size of the exchanger was also optimized to maximize the net gain.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.26 no.1
• /
• pp.48-54
• /
• 2014

A refrigeration dehumidifier with a recuperative heat exchanger is theoretically analyzed. The recuperative heat exchanger is located between the two air streams from and to the dehumidifying coil, and reduces the sensible heat load in dehumidification process. A simple model is developed to predict performance of the dehumidifier. The model predicts that the recuperative heat exchanger is effective especially in the low humidity condition, where the sensible heat load is relatively large. It is predicted that, by adopting a recuperative heat exchanger, a maximum 30~110% increase in COP is possible for indoor air at $27^{\circ}C$, and 40~60% relative humidity.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1997.10a
• /
• pp.105-113
• /
• 1997

보일러 연도 배기가스 현열을 회수하여 연료가스인 BFG를 예열하기 위한 분리형 열파이프 시스템을 개발하였다. BFG 예열 시스템의 열설계를 위한 전열모델을 수립하고 설계를 위한 프로그램을 작성하였으며 3,700KW급의 실규모 설비를 제작하여 현장적용 시험을 수행하였다. 개발시스템에 대한 실조업 성능평가를 행하여 보일러 운전에 미치는 영향, 시스템 자체의 성능 및 작동특성, 운전과 유지보수성에 대한 종합적인 검토를 수행하였으며 본 시스템의 적용을 통하여 보일러의 열효율이 평균 4% 향상되는 것으로 나타났다. 실조업 평가를 통하여 본 개발 시스템이 BFG의 예열을 위한 최적의 시스템인 것으로 판단되었다.